This invention relates generally to a d.c. power source whose output voltage level or output power can be continuously varied, and particularly to a d.c. power source suitable for use in microwave ovens.
The d.c. power supply according to the present invention can be used not only for microwave ovens, but also for various kinds of apparatus which require a high voltage d.c. power source. For simplicity of explanation, the present description will be directed to a d.c. power supply to be used for driving a magnetron in a microwave oven; however, other applications of the present invention will be apparent therefrom.
Most microwave ovens which have been marketed to date use a d.c. power supply comprising a transformer for boosting the commercial a.c. voltage and a full-wave voltage rectification circuit for rectifying the boosted voltage. Such a d.c. power supply is relatively simple in its circuit configuration; however, it needs smoothing condensers of large capacity to obtain a d.c. voltage having a flat waveform. As a result, the d.c. power source accounts for a large part of the configuration of the microwave oven in both weight and volume. This fact causes a problem in the manufacture of small-sized microwave ovens.
In order to control the output power, the well-known d.c. power source has a plurality of condensers selectively connected with the full-wave voltage rectifier, so that the switching over of the connection of the condensers will change the output power in a stepwise manner. It is desirable, however, for the good cook of various kinds of foods which are different in shape and comprise different components to be able to continuously control the output power of the oven over a wide range.